Device for introducing an additive into an exhaust gas

ABSTRACT

A reducing agent or an additive that releases an agent is often added to an exhaust gas from engines in order to chemically convert constituents, in particular nitrogen oxides, in the exhaust gas. To achieve intimate mixing of the exhaust gas with the reducing agent or additive over a short section of the gas duct, at least one mixer and at least one nozzle for introducing the additive into the exhaust gas are structurally and functionally combined with one another.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of copending InternationalApplication PCT/DE00/02402, filed Jul. 21, 2000, which designated theUnited States.

BACKGROUND OF THE INVENTION Field of the Invention

[0002] The invention relates to a device for introducing an additiveinto an exhaust gas or gas stream, which can be introduced into a gasduct, in particular into an exhaust gas line from a diesel engine. Thedevice has at least one nozzle and at least one mixer. The additive maybe a reducing agent or a compound that releases such an agent.

[0003] A device of this type is known, for example, from Published,Non-Prosecuted German Patent Application DE 36 42 612 A. The deviceintroduces a reducing agent into a NOx-containing exhaust-gas duct withintensive mixing. The device is intended to achieve a homogeneous mixingof the reducing agent and the exhaust gas over a relatively shortsection of duct.

[0004] High levels of efficiency are desired during the conversion offossil fuel or of fuel obtained from plants into mechanical and/orthermal energy. The conversion temperatures are often so high thatsignificant amounts of nitrogen oxides (NOx) are formed during theconversion (combustion). This applies in particular to diesel engines,which are operated, for example with mineral oil or with rapeseed oil.

[0005] Since a release of the nitrogen oxide is extremely undesirableand is therefore to be avoided, the nitrogen oxides are usuallycatalytically reduced. However, this requires the presence of a reducingagent in the exhaust gas from an energy conversion installation, forexample, in a diesel engine. It has proven expedient to admix a reducingagent of this type or an additive that releases it as a reducing-agentcarrier, in particular ammonia or urea (dissolved in water), to theexhaust gas only after it has emerged from the energy conversioninstallation.

[0006] During operation of a device of this type or of a flue-gascleaning device, it is often difficult to achieve sufficiently intimatemixing of the exhaust gas or gas stream with the reducing agent. Thereason for this is that the length of the gas or exhaust gas duct whichis inherently required to achieve this, being of the order of magnitudeof approximately 50 times the duct diameter, is not realistic. Forrelatively small installations, such as for example diesel engines withan output of up to a few 100 kW, it is in principle possible to feed areducing agent carrier into the exhaust-gas duct via an injectiondevice, for example via a single nozzle, and a reducing-agent generatorwhich lies close behind the engine. However, as the rated output rises,this entails disproportionately high costs.

[0007] In relatively large installations, for example, in a combinedheat and power plant or a drive of a ship, with exhaust-gas ductdiameters of over 200 mm, therefore, it is usual for at least two staticmixers to be disposed downstream of an atomization system, whichrepresents a complex injection device. The distances between theatomization system and the mixers are in each case to be at least equalto twice the diameter of the exhaust-gas duct. However, space for theresulting length of exhaust-gas duct is often not available.

SUMMARY OF THE INVENTION

[0008] It is accordingly an object of the invention to provide a devicefor introducing an additive into an exhaust gas which overcomes theabove-mentioned disadvantages of the prior art devices of this generaltype, which allows the use both of an injection device or at least onenozzle for an additive and of a number of necessary mixers in anexhaust-gas duct in which, at the same time, the duct length is as shortas possible. It should be possible for the device to be used inparticular in a round gas duct whose diameter is between approximately200 mm and approximately 1000 mm.

[0009] With the foregoing and other objects in view there is provided,in accordance with the invention, a device for introducing an additiveinto an exhaust gas. The exhaust gas is introduced into an exhaust gasline from a diesel engine and has a flow direction. The device containsat least one nozzle, and at least one mixer for mixing the exhaust gaswith the additive. The mixer and the nozzle combined with one anotherform a structural and functional unit. The mixer has a tubular bodydisposed approximately parallel in terms of the flow direction of theexhaust gas and houses the nozzle. The tubular body has an upstream endwith a first opening formed therein and a downstream end with a secondopening formed therein and communicates with the first opening. Themixer has lamellae supported by the tubular body, and the lamellae, withregard to the flow direction of the exhaust gas, face upstream at theupstream end of the tubular body and face downstream at the downstreamend of the tubular body.

[0010] For this purpose, the mixer and the nozzle for atomizing theadditive or the reducing agent itself are combined to form a structuraland functional unit. The combination can be introduced into the gasduct, i.e. can be fitted into the duct when the structural unit isoperating as intended.

[0011] This immediately eliminates the length of the distance from thenozzle to the mixer of a first mixer stage, so that the duct length canpreferably be shortened to only two to four times the duct diameter (twoto four duct diameters). Neither the action nor the efficiency of eachindividual functional part, namely the injection function, on the onehand, and the static mixer function, on the other hand, is impaired.

[0012] According to an expedient refinement, the mixer has a tubularbody which is open at both ends, is parallel in terms of flow, isadvantageously, in the installed state, coaxial with respect to the gasduct and at one end bears lamellae which face upstream and at the otherend bears lamellae which face downstream. In this case, the tubularbody, in a gas duct that is circular in cross section, is likewisecircular in cross section. The diameter of the gas duct into which thestructural unit containing the mixer and the nozzle can be fitted shouldexpediently be no less than approximately 200 mm and no greater thanapproximately 1000 mm.

[0013] In advantageous configurations of the tubular body, its diameteris approximately 0.5 to 0.2 times the diameter of the gas duct. Thelength of the tubular body approximately corresponds to 0.2 to 0.5 timesthe diameter of the gas duct. In this case, the tubular body isexpediently supported by a tubular connection piece that projects intothe gas duct transversely with respect to the gas stream and throughwhich a tube, which serves as a feed line and as a support for thenozzle or the injection device, extends as far as the center axis of thetubular body.

[0014] The nozzle is advantageously disposed in the region of the centeraxis of the tubular body, and therefore, in the installed state, of thecenter axis which is common to the gas duct and the tubular body. Inthis position, the nozzle or the injection device atomizes the additive,for example ammonia as the reducing agent or urea solution as theadditive, in the direction of flow of the gas stream. A spray cone thatemerges from the nozzle includes an angle of 20° to 60°, preferably anangle of 30°, at its cone tip.

[0015] Lamellae that are supported at the ends of the tubular bodypreferably form an angle of from 30° to 60°, in particular an angle of45°, with the axis of the tubular body. The lamellae are oriented insuch a manner that, in the installed state of the device, they aresupported on the inner side of walls of the gas duct by their free ends.In this case, the lamellae are approximately twice as wide at their freeends as at their root ends that are connected to the tubular body. Freespaces between adjacent lamellae are in this case approximately as wideas the lamellae themselves.

[0016] Expediently, the lamellae which face upstream are staggered withrespect to the lamellae which face downstream, so that every partialstream of the gas stream is made turbulent, in each case an identicalnumber of the lamellae which face downstream and the lamellae which faceupstream are provided. The tubular body expediently bears in each casefour to eight lamellae at both end sides, the lamellae preferably areformed of planar metal sheets.

[0017] The advantages which are achieved with the invention consist inparticular in the fact that, on account of the spatial and functionalcombination of at least one mixer and the nozzle in a device which hasthese functional components for the introduction of an additive, such asfor example ammonia or urea solution, into an exhaust gas, it ispossible to achieve a particularly short configuration of an exhaust-gasduct accommodating the device, without the risk of the mixer becomingencrusted, even when using urea solution.

[0018] The reason for this is that only a short trailing section in theexhaust-gas duct is required even though, at the same time, it isensured that the temperature and velocity are made more uniform over theentire cross section of the duct.

[0019] Moreover, the small number of components in the overall systemleads to a reduction in manufacturing costs.

[0020] Other features which are considered as characteristic for theinvention are set forth in the appended claims.

[0021] Although the invention is illustrated and described herein asembodied in a device for introducing an additive into an exhaust gas, itis nevertheless not intended to be limited to the details shown, sincevarious modifications and structural changes may be made therein withoutdeparting from the spirit of the invention and within the scope andrange of equivalents of the claims.

[0022] The construction and method of operation of the invention,however, together with additional objects and advantages thereof will bebest understood from the following description of specific embodimentswhen read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a diagrammatic, partially, longitudinal sectional-viewof a flue-gas cleaning device with a combined mixing and injectiondevice according to the invention;

[0024]FIG. 2 is a partially sectional plan view of the cleaning device;

[0025]FIG. 3 is a front-elevational view of the cleaning device;

[0026]FIG. 4 is a sectional view of the cleaning device taken along theline IV-IV shown in FIG. 1; and

[0027]FIG. 5 is a sectional view of the cleaning device taken along theline V-V shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] In all the figures of the drawing, sub-features and integralparts that correspond to one another bear the same reference symbol ineach case. Referring now to the figures of the drawing in detail andfirst, particularly, to FIG. 5 thereof, there is shown a gas orexhaust-gas duct 1 with a diameter d1 of, for example, 200 mm to 1000 mmis connected, by a flange 2 (FIG. 1) to a preferably non-illustratedstationary diesel engine. An exhaust gas A flows through it in thedirection indicated by an arrow 3. A tubular connection piece 4penetrates through a wall of the exhaust-gas duct 1 and projects intothe exhaust-gas duct 1 transversely with respect to the direction offlow 3 of the exhaust-gas A and therefore at right angles to a duct axis5. If the duct cross section is circular, as in the exemplaryembodiment, therefore, the tubular connection piece 4 runs in a radialdirection. Outside the exhaust-gas duct 1, the tubular connection piece4 bears a flange 6 at its free end, on which an end plate 7 rests in asealed manner, thus closing off an interior of the tubular connectionpiece 4 with respect to the outside.

[0029] That end of the tubular connection piece 4 which lies in theexhaust-gas duct 1 bears a tubular body 8 which is open at both endsides and is disposed coaxially with respect to the exhaust-gas duct 1.The duct axis 5 therefore forms the center axis of both the exhaust-gasduct 1 and the tubular body 8. The tubular body 8 has a diameter d2(FIG. 5) that corresponds to 0.2 to 0.5 times the diameter d1 of theexhaust-gas duct 1.

[0030] The tubular body 8 has a length that is approximately equal to0.2 to 0.5 times the diameter d1 of the exhaust-gas duct 1.

[0031] A number of first lamellae 9, which face upstream with respect tothe direction of flow 3 of the exhaust gas A, are secured to aninflow-side end of the tubular body 8. A preferably identical number ofsecond lamellae 10, which correspondingly extend downstream, are securedto an outflow-side end of the tubular body 4. The lamellae 9 and thelamellae 10 are disposed staggered with respect to one another, i.e.each of the lamellae 9 lies between in each case two lamellae 10, andvice versa, as seen in the direction of the duct axis 5. This can beseen relatively clearly from FIGS. 3 to 5.

[0032] The lamellae 9 and 10 in each case form an angle α from 30° to60°, preferably of α=45° (see FIG. 1), with the duct axis 5 and aresupported, by their free ends 9 a and 10 a, respectively, on the innerside or inner wall 1′ of the exhaust-gas duct 1. The free ends 9 a, 10 aof the lamellae 9 and 10 are approximately twice as wide as their rootends 9 b and 10 b, respectively, which are secured to the tubular body8. By way of example, four to eight lamellae 9, 10 are secured to eachend of the tubular body 8, the lamellae 9, 10 contain planar metalsheets. Consequently, they cause particularly powerful turbulence in theflowing exhaust gas A.

[0033] The tubular connection piece 4 contains a tube 11 that issupported by the end plate 6 and on which, at a free end side in thetubular body 8, a nozzle 12 is held. The tube 11 is connected via aline, in a manner which is not illustrated in more detail, to areservoir for an additive which releases a reducing agent or for areducing-agent carrier R, for example for an aqueous urea solution, andexpediently, in addition, to an air connection for cooling and atomizingthe urea solution which is, for example, aqueous. A non-illustrated pumpforces the reducing-agent carrier R, e.g. the aqueous urea solution, ora corresponding reducing agent, e.g. ammonia, through the tube 11 andthrough the nozzle 12.

[0034] The geometric dimensions of the nozzle 12 are such that, at thedelivery pressure of the reducing-agent carrier R which is reached, aspray cone 13 is formed by the carrier R when it emerges from the nozzle12, the tip of which cone includes an angle β of from 20° to 60°,preferably of β=30° to 45°. The nozzle 12 and the tubular body 8 withthe lamellae 9 and 10 therefore form a structural and functional unit,the tubular body 8 and the lamellae 9, 10 attached thereto representing,in functional terms, a static mixer or a mixing stage. The nozzle 12 inthis case lies on the common center axis of the exhaust-gas duct 1 andof the mixer 8, 9, 10, which corresponds to the duct axis 5.

[0035] In operation, the hot exhaust gas A from the diesel engine flowsthrough the exhaust-gas duct 1 in the direction of flow 3. In theprocess, a small proportion of the exhaust gas A, and therefore at leastone exhaust-gas partial stream, flows through the tubular body 8. When apredetermined operating state is reached, the reducing-agent carrier Ris sprayed or injected through the nozzle 12 into the flowing exhaustgas A.

[0036] In the region of the tubular body 8, considerable turbulencecaused by the lamellae 9 and 10 occurs in the flowing exhaust gas A,which turbulence also acts on the spray cone 13, thus ensuring veryintimate mixing of the exhaust gas A with the reducing-agent carrier R.

[0037] In the state which prevails in the exhaust-gas duct 1, the, forexample, aqueous urea solution is broken down by hydrolysis into gaseousammonia and water, so that in the gas mixture which is formed in thisway, when a catalytic converter which is suitable and provided for thispurpose, but is not shown, is reached, nitrogen oxides contained in theexhaust gas A are virtually completely reduced to form nitrogen.

We claim:
 1. A device for introducing an additive into an exhaust gas,the exhaust gas being introduced into an exhaust gas line from a dieselengine and having a flow direction, the device comprising: at least onenozzle; and at least one mixer for mixing the exhaust gas with theadditive, said mixer and said nozzle combined with one another to form astructural and functional unit, said mixer having a tubular bodydisposed approximately parallel in terms of the flow direction of theexhaust gas and housing said nozzle, said tubular body having anupstream end with a first opening formed therein and a downstream endwith a second opening formed therein and communicating with said firstopening, said mixer having lamellae supported by said tubular body, andsaid lamellae, with regard to the flow direction of the exhaust gas,face upstream at said upstream end of said tubular body and facedownstream at said downstream end of said tubular body.
 2. The deviceaccording to claim 1, wherein said tubular body has a cross section thatis circular.
 3. The device according to claim 1, wherein said tubularbody has a diameter in a range of 0.2 to 0.5 times a diameter of theexhaust gas line.
 4. The device according to claim 1, wherein saidtubular body has a length that is approximately 0.2 to 0.5 times adiameter of the exhaust gas line.
 5. The device according to claim 1,wherein said mixer has a tubular connection piece projecting into theexhaust gas line and guided onto said tubular body, said mixer furtherhaving a tube serving as a feed line and as a support for said nozzle,said tube extending into said tubular body through said tubularconnecting piece.
 6. The device according to claim 1, wherein mixer hasa center axis and said nozzle lies on said center axis in such a mannerthat the additive can be sprayed in the flow direction of the exhaustgas.
 7. The device according to claim 1, wherein said tubular body hasan axis, and said lamellae supported by said upstream end and saiddownstream end of said tubular body form an angle of 30° to 60°, withsaid axis of said tubular body and, said lamellae for support, have freeends directed onto an inner side of the exhaust gas line.
 8. The deviceaccording to claim 1, wherein said lamellae have root ends connected tosaid tubular body and free ends being approximately twice as wide assaid root ends.
 9. The device according to claim 1, wherein saidlamellae have a given width, and between adjacent ones of said lamellaefree spaces are formed having a width approximately as wide as saidgiven width of said lamellae.
 10. The device according to claim 1,wherein said lamellae that face upstream are disposed staggered withrespect to said lamellae that face downstream.
 11. The device accordingto claim 1, wherein a number of said lamellae facing upstream is equalto a number of said lamellae facing downstream.
 12. The device accordingto claim 1, wherein said tubular body bears a same number of saidlamellae at both of said upstream end and said downstream end.
 13. Thedevice according to claim 1, wherein said lamellae include planar metalsheets.
 14. The device according to claim 12, wherein said tubular bodybears between four and eight of said lamellae at both of said upstreamend and said downstream end.
 15. The device according to claim 7,wherein said angle is 45°.